POS0659 COMPARISON OF METROLOGICAL PROPERTIES OF THE S-SCAISS VERSUS THE SPARCC SCORING SYSTEM FOR THE DETECTION/QUANTIFICATION OF INFLAMMATION AT MRI-SIJ IN SPONDYLARTHRITIS: DATA FROM THE DESIR COHORT
Authors: R. Almodovar González, P. Zarco-Montejo, A. Bueno, C. García-Monco, E. Pérez-Fernández, C. López-Medina, M. Dougados, R. Mazzucchelli
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Different tools to quantify inflammatory changes in sacroiliac (SI) MRI have been developed. The Spondyloarthritis Research Consortium of Canada (SPARCC) appears to be the most sensitive to change, as it has demonstrated a good discriminating capacity. In a previous work of our group, we described the development of a fast, easy and reliable method to quantify the bone marrow edema (BME) in MRI-SIJ, through a semi-automatic process with a computer tool called SCAISS. SCAISS uses both semi-axial and semi-coronal slices from the MRI-SIJ. Since many centres only perform semi-coronal slices, we developed a simplified tool (s-SCAISS) that only requires the assessment of semi-coronal slices. <h3>Objectives</h3> To compare inter-rater reliability, discriminative validity and sensitivity to change using the s-SCAISS system, and compared to the SPARCC system, in patients presenting with inflammatory low back pain suggestive of axial spondyloarthritis from the DEvenir des Spondylarthopathies Indifférenciées Récentes (DESIR) cohort. <h3>Methods</h3> MRI-SIJ image of 206 patients collected at baseline of the DESIR cohort and after a first one year follow-up were analyzed (46.6% male, mean age 33.6 ± 8.8 years). Inter-reader reliability (3 readers for s-SCAISS and 2 central core readers for SPARCC) was assessed using intraclass correlation coefficients (ICC). Discriminative validity testing was performed by calculating the Area Under the Curve (AUC), sensitivity, specificity and likelihood ratios for different cut-off points for the classification of presence/absence of BME in SI, using positive/negative MRI as the gold standard according to DESIR core readers. Sensitivity to change was evaluated in subjects with improvement in illness activity testing differences between paired measures. Three different criteria were considered to define activity improvement: a change in ASDAS score at 12 months of 1.1 (Clinical Important Improvement -CII-) and 2 points (Major Improvement -MI-) and a reduction ≥ 50% of the initial BASDAI score (BASDAI50). <h3>Results</h3> <b>Inter-rater reliability:</b> Both s-SCAISS and SPARCC showed good inter-reader reliability: In baseline MRI: ICC 0.95 and 0.82, respectively; At 1 year MRI: ICC 0.80 and 0.79, respectively. <b>Discriminative validity</b>: Of the 206 patients included in our study, 70 (34%) fulfilled the ASAS criteria for presence of Inflammation on MRI, The AUC for EMO detection was excellent for both systems (0.88 and 0.98 for SCAISS and SPARCC, respectively). The optimal cut-off point for s-SCAISS was 60 u (Sens 83%, Esp 80%) and for SPARCC 1.25 u (Sens 93% and Esp 94%). Using the s-SCAISS cut-off point of 60 u, and the one 1.25 for SPARCC, 165 patients (81.3%) and 189 patients (93.1%), respectively were classified in accordance with the ASAS definition of the presence or absence of inflammation at MRI evaluated by the human central readers. <b>Sensitivity to change</b>: Of the 206 patients included, at 1 year after baseline assessment, 48 (23.3%), 17(8.3%) and 54 (26.2%) patients had a CII, MI and BASDAI50, respectively. In these patients with improved disease activity, the mean (SD) s-SCAISS score at baseline was 404.1 (SD 1055.1), 185.7 (262.7) and 375.3 (SD1008.8), respectively. While at 12 months it decreased to 72.6 (SD134.8), 46.1 (SD72.1) and 76 (SD151.7). The means of paired differences were 331.4 (SD 1019.6), 139.7 (SD 240.8) and 298.3 (SD 976.9), respectively, all of them with p&lt;0.05. As expected, the AUC for the detection of CII, MI and BASDAI50 for both systems were poor (s-SCAISS 0.61, 0.63 and 0.58 and for SPARCC 0.7, 0.66, 0.60, respectively). <h3>Conclusion</h3> The MRI-SIJ EMO quantification system with s-SCAISS is as reliable and sensitive to change as SPARCC. The apparent advantage of SPARCC over s-SCAISS is artefactualised by the fact that the definition of the presence or absence of ASAS criteria for sacroiliitis is determined by the same readers who assess SPARCC. <h3>Acknowledgements</h3> We thank all DESIR-cohort patients and all individuals involved with creating and maintaining the cohort. The DESIR cohort was sponsored by the Département de la Recherche Clinique et du Développement, Assistance Publique Hôpitaux de Paris. We are also grateful to the heads of the participating regional centres. <h3>Disclosure of Interests</h3> None Declared.